Method of injection well stimulation

ABSTRACT

Stimulation of injection walls in a heterogeneous reservoir (i.e., characteristically having differing permeability streaks) is improved by temporarily or permanently sealing off the highly permeable streaks with plugging agents and then stimulating the well with a micellar dispersion. This process provides a more uniform profile of the relative permeability of water flowing in the reservoir.

States atent [191 Milton, Jr.

[ METHOD OF INJECTION WELL STIMULATION [75] Inventor: Harry W. Milton,Jr., Findlay, Ohio [73] Assignee: Marathon Oil Company, Findlay,

Ohio

[22] Filed: Feb. 8, 1971 [21] Appl. No.: 113,720

Kennedy Kiel et al. ..166/269 X 1 Feb. 27, 1973 3,251,414 5/1966 Willman..l66/269 X 2,402,588 6/ l 946 Andresen 1 66/270 3,254,714 6/1966Gogarty et al ..l66/274 3,506,070 4/1970 Jones ..166/273 3,482,63112/1969 Jones ..166/273 3,174,546 3/1965 Flickinger 166/269 PrimaryExaminerStephen J. Novosad Attorney-Joseph C. Herring, Richard C.Wilson, Jr. and Jack L. Hummel [57] ABSTRACT Stimulation of injectionwalls in a heterogeneous reservoir (i.e., characteristically havingdiffering permeability streaks) is improved by temporarily orpermanently sealing off the highly permeable streaks with pluggingagents and then stimulating the well with a micellar dispersion. Thisprocess provides a more uniform profile of the relative permeability ofwater flowing in the reservoir.

21 Claims, No Drawings METHOD OF INJECTION WELL STIMULATION BACKGROUNDOF THE INVENTION 1. Field of the Invention This invention relates to thesecondary recovery of petroleum, particularly to an improved method ofinjection well stimulation. That is, the injectivity index is improvedby this invention.

2. Description of the Prior Art In order to economically effect a goodwaterflood operation, water should be injected into the reservoir at ahigh rate and it should flow uniformly, i.e., without fingering,throughout the reservoir. In a heterogeneous reservoir, characteristicof highly permeable streaks, the water will tend to flow through thestreaks creating a fingering effect. Unless these streaks are plugged, alarge portion of the reservoir oil will be left in place.

The water injection rate is limited by the high pressure drop in thereservoir immediately surrounding the wellbore. This pressure drop isdue to skin damage, residual oil saturation in this area, etc. Bydisplacing this oil and removing the skin damage, water injection ratescan be increased.

U. S. Pat. No. 3,443,640 to Klein teaches selective plugging of asubsurface formation using a solution of minute solid particles and adispersing surfactant. The solution is injected into the permeabilitystreaks and allowed to settle, permitting the solid particles toprecipitate from the solution.

U. S. Pat. No. 3,039,529 to McKennon teaches the use of partiallyhydrolyzed acrylamide polymers as viscosity increasing agents in thesecondary recovery of petroleum.

U. S. Pats. Nos. 3,467,188 and 3,474,865 to Gogarty teach the use ofmicellar dispersions to increase the injectivity index of an injectionwell. These dispersions reduce the residual hydrocarbon saturation inthe sandpores immediately adjacent the wellbore and remove the skindamage from the face of the wellbore.

SUMMARY OF THE INVENTION Applicant has developed a process whereby crudeoil is economically and efficiently produced from a heterogeneoussubterranean oil-bearing formation. This process comprises injectinginto the formation plugging agents, which penetrate zones of highpermeability, and then injecting a micellar dispersion into theformation immediately surrounding the wellbore. The plugging agents andthe micellar dispersion may be injected separately or in the same slug.As a result, a more uniform profile of the reservoir rock or formationwill be stimulated, and the reservoir will be more receptive to highwater injection rates. A larger volume of crude oil will therefore beproduced from a production means as a result of increased injectivityindexes of the injection wells.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The term permeability streak,as used in this invention, is a channel created by either a fracturenetwork or a zone of high permeability. A high permeability zone in thisrespect is often referred to as a matrix.

Plugging agents which can be used in conjunction with this inventioninclude finely-powderedsolids, such as cement, colloidal clays, and waxdistillates mixed with water; various forms of plastics; gel-formingmixtures of silicic acid; mixtures of urea formaldehyde resin; andothers. (See Selective Plugging by Chemical Methods by Dr. H. C. Lawton,The Oil Weekly, May 19, 1947); (also see New Matrix Scaling and FluidDiversion Systems Find Application in Both 1njection and Producing Wellsby J. P. Morgan et al., The Journal of Canadian Petroleum Technology,April to June, 1967.)

Preferably the plugging agents are high molecular weight, syntheticorganic polymers. Specific examples of these polymers includepolyacrylamides; polysaccharides; polyalkane oxides; partiallyhydrolyzed polyacrylamides and their derivatives, including acrylamideswhich have been substituted with functional groups such as sulfonategroups, phosphate groups, and the like. Also, partially hydrolyzedcopolymers of polyacrylamides and their derivatives, e.g., copolymerswith vinyl sulfonates, vinyl phosphates, and vinyl acrylides; andderivatives of polysaccharides, e.g., carboxymethyl cellulose andcellulose derivatives, dextran, starch derivatives, etc. are useful.Molecular weights of the above-named polymers can range from about 10 10or more, depending upon the specific characteristics of the permeabilitystreaks to be plugged.

The mobility of the above-named polymers may be varied by blending withwater. Preferably fresh water or brackish water should be used as thesolute; the brackish water can be used to increase the mobility ofcertain polymers, if desired.

- About 0.1 50 or more barrels of plugging agent per vertical foot ofoil-bearing sand is useful to plug the permeability streaks. Preferably,about 1 25 barrels are sufficient.

The micellar dispersion used in this invention may be characterized aseither oil-external or water-external. Examples of such dispersions canbe found in U. S. Pat. Nos. 3,467,188 and 3,474,865 to Gogarty andGogarty et 2.1. respectively.

The micellar dispersion contains hydrocarbon, aqueous medium, surfactantsufficient to impart micellar characteristics to the hydrocarbon andaqueous medium, and optionally cosurfactant(s) and/or electrolyte(s).Examples of volume amounts include about 1 to about percent hydrocarbon,about 5 to about percent aqueous medium, at least about 4 percentsurfactant, about 0.01 to about 20 percent cosurfactant, and about 0.001to about 4 percent by weight of the electrolyte. Also, the micellardispersion can con tain other additives such as corrosion inhibitingagent, bactericides, etc. Examples of the hydrocarbon, aqueous medium,surfactant, the cosurfactant, and the electrolyte are found in U. S.Pat. Nos. 3,254,714 and 3,275,075 to Gogarty et al.; 3,497,006 to Joneset al.; and US. Pat. Nos. 3,470,958 and 3,467,194 to Kinney.

The mobility of the oil-external micellar dispersion can be about equalto or greater than the mobility of the formation fluids (i.e.,combination of oil and water within the formation).

The amount of micellar dispersion injected into the formation preferablyis about 0.01 to about 10 barrels and more preferably about 0.1 to about5 barrels per vertical foot of oil-bearing sand.

The micellar dispersion is preferably injected at a pressure less thanthe formation fracture pressure. After the dispersion is injected intothe formation, it can remain in contact with the area immediatelyadjacent the wellbore for times up to about 6 hours and more preferablyfor about 12 hours. Such contact times insure a more completesolubilization of the residual oil, etc., allowing for better cleansingof the porous rock.

Optionally, the plugging agents and the micellar dispersion may beinjected into the formation separately or in the same slug. When the twocomponents are injected in the same slug, the plugging agents comprisethe front portion, about 1 50 percent by volume, while the micellardispersion comprises the remainder of the slug.

The wellbore in fluid communication with the subterranean formation maybe either cased or uncased. If the wellbore is cased, sealer balls,known in the fracturing art, may be used to effect an improved profileby injecting the sealer balls intermittently with the plugging agent.

It should be understood that the invention is capable of a variety ofmodifications and variations which will be made apparent to thoseskilled in the art by a reading of the specification and which are to beincluded within the spirit of the specification and appended claims.

What is claimed is:

1. A process for improving the injectivity index of an injection well influid communication with an oil-bearing, heterogeneous, subterraneanformation having highly permeable streaks immediately adjacent saidinjection means, the process comprising:

a. injecting into the formation an aqueous solution containing aplugging agent in an amount sufficient to effectively plug the highlypermeable streaks in the formation, then b. injecting into the formationabout 0.01 to about barrels of a micellar dispersion per vertical footof oil-bearing formation, and

c. displacing the micellar dispersion out into the formation byinjecting water.

2. The process of claim 1 wherein said injection means is a casedwellbore.

3. The process of claim 1 wherein said injection means is an uncasedwellbore.

4. The process of claim 1 wherein about 0.1 to about 50 barrels pervertical foot of oil-bearing formation of the aqueous solutioncontaining the plugging agent is injected into the formation.

5. The process of claim 1 wherein said micellar dispersion ischaracterized as water-external.

6. The process of claim 1 wherein said micellar dispersion ischaracterized as oil-external.

7. The process of claim 1 wherein the micellar dispersion is comprisedof hydrocarbon, aqueous medium and surfactant.

tive thereof oracombination thereof.

10. The process of claim 1 wherein the micellar dispersion is comprisedof about 1 to about percent by volume hydrocarbon, about 5 to aboutpercent by volume of aqueous medium, and at least about 4 percent byvolume of surfactant.

11. A process for recovering crude oil from an oilbearing subterraneanheterogeneous formation having at least one injection means in fluidcommunication with at least one production means and wherein theformation has highly permeable streaks immediately adjacent saidinjection means, the process comprising:

a. injecting into the formation about 0.01 to about 10 barrels of amicellar dispersion per vertical foot of oil-bearing formation, thefront portion of the micellar dispersion containing a plugging agent inamounts sufficient to effectively plug the highly permeable streaks inthe formation, and

b. displacing this micellar dispersion toward the production means torecover crude oil therethrough.

12. The process of claim 11 wherein the plugging agent in the frontportion of the micellar dispersion represents about 1 to about 50% byvolume of the dispersion.

13. The process of claim 11 wherein said injection means is a casedwellbore.

14. The process of claim 11 wherein said injection means is an uncasedwellbore.

15. The process of claim 11 wherein the micellar dispersion ischaracterized as being water-extemal.

16. The process of claim 11 wherein the micellar dispersion ischaracterized as being oil-external.

17. The process of claim 11 wherein the micellar dispersion is displacedtoward the production means with water.

18. The process of claim 11 wherein the micellar dispersion is comprisedof hydrocarbon, aqueous medium and surfactant.

19. The process of claim 11 wherein the plugging agent is a highmolecular weight, synthetic organic polymer.

20. The process of claim 19 wherein the organic polymer is apolyacrylamide, a partially hydrolyzed polyacrylamide or a derivativethereof, a partially hydrolyzed copolymer of polyacrylamide or aderivative thereof or a combination thereof.

21. The process of claim 11 wherein the micellar dispersion is comprisedof about 1 to about 85 percent by volume hydrocarbon, about 5 to about95 percent by volume of aqueous medium, and at least about 4 percent byvolume of surfactant.

2. The process of claim 1 wherein said injection means is a casedwellbore.
 3. The process of claim 1 wherein said injection means is anuncased wellbore.
 4. The process of claim 1 wherein about 0.1 to about50 barrels per vertical foot of oil-bearing formation of the aqueoussolution containing the plugging agent is injected into the formation.5. The process of claim 1 wherein said micellar dispersion ischaracterized as water-external.
 6. The process of claim 1 wherein saidmicellar dispersion is characterized as oil-external.
 7. The process ofclaim 1 wherein the micellar dispersion is comprised of hydrocarbon,aqueous medium and surfactant.
 8. The process of claim 1 wherein theplugging agent is a high molecular weight, synthetic organic polymer. 9.The process of claim 8 wherein the organic polymer is a polyacrylamide,a partially hydrolyzed polyacrylamide or a derivative thereof, apartially hydrolyzed copolymer or a polyacrylamide or a derivativethereof or a combination thereof.
 10. The process of claim 1 wherein themicellar dispersion is comprised of about 1 to about 85 percent byvolume hydrocarbon, about 5 to about 95 percent by volume of aqueousmedium, and at least about 4 percent by volume of surfactant.
 11. Aprocess for recovering crude oil from an oil-bearing subterraneanheterogeneous formation having at least one injection means in fluidcommunication with at least one production means and wherein theformation has highly permeable streaks immediately adjacent saidinjection means, the process comprising: a. injecting into the formationabout 0.01 to about 10 barrels of a micellar dispersion per verticalfoot of oil-bearing formation, the front portion of the micellardispersion containing a plugging agent in amounts sufficient toeffectively ''''plug'''' the highly permeable streaks in the formation,and b. displacing this micellar dispersion toward the production meansto recover crude oil therethrough.
 12. The process of claim 11 whereinthe plugging agent in the front portion of the micellar dispersionrepresents about 1 to about 50% by volume of the dispersion.
 13. Theprocess of claim 11 wherein said injection means is a cased wellbore.14. The process of claim 11 wherein said injection means is an uncasedwellbore.
 15. The process of claim 11 wherein the micellar dispersion ischaracterized as being water-external.
 16. The process of claim 11wherein the micellar dispersion is characterized as being oil-external.17. The process of claim 11 wherein the micellar dispersion is displacedtoward the production means with water.
 18. The process of claim 11wherein the micellar dispersion is comprised of hydrocarbon, aqueousmedium and surfactant.
 19. The process of claim 11 wherein the pluggingagent is a high molecular weight, synthetic organic polymer.
 20. Theprocess of claim 19 wherein the organic polymer is a polyacrylamide, apartially hydrolyzed polyacrylamide or a derivative thereof, a partiallyhydrolyzed copolymer of polyacrylamide or a derivative thereof or acombination thereof.
 21. The process of claim 11 wherein the micellardispersion is comprised of about 1 to about 85 percent by volumehydrocarbon, about 5 to about 95 percent by volume of aqueous medium,and at least about 4 percent by volume of surfactant.